Method of coating a spray wheel



7 June 28, 1960 E. w. mzwcoma 2,942,998

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Filed lay 27, 1957 l O O unmlmm|n:|lllllllmum ll INVENTOR (fl emit W/Vawomb Arms United States Patent METHOD OF COATING A SPRAY WHEEL Everett W. Newcomb, Roselle, N.J., assignor to Georgia Kaolin Company, Elizabeth, NJ., a corporation of New Jersey Filed May 27, 1957, Ser. No. 661,813

1 Claim. (Cl. 11749) This invention relates to a method of coating objects which when in use are customarily subjected to stresses of great magnitude. Many objects are coated with protective materials to preserve them from the effects of high temperatures, abrasion and other deteriorating forces. If the object is subject to stresses of great magnitude when in use, there is often a tendency on the part of the coating material to chip off and thus to leave portions of the surface of the object unprotected. An example of such behaviour is found in spray wheels such as are used in apparatus for drying clay slurries. Such wheels are ordinarily six to seven inches in diameter and are rotated at high speeds, that is, speeds of the order of 5,000 to 13,000 rpm. Such speeds impose on the material of the wheel substantial internal stresses which are apt to result in a chipping of portions of a coating of metal oxide which has been applied to the surface of the wheel to protect it from undue abrasion by the rubbing of the clay particles in the slurry which is fed to the wheel. I have found that by prmtressing the wheel by rotating it at the operating speed for a suflicient time to stretch the metal in the wheel centrifugally to a point where it takes a certain set, and thereafter applying the coating of metal oxide in the usual manner, the useful life of the coating is greatly increased.

On the drawing:

Figure 1 is a perspective view of a typical spray wheel for spraying clay slurries; and

Figure 2 is a fragmentary radial section of the wheel shown in Figure 1.

The wheel shown on the drawing consists essentially of a disk 10 the upper face of which is concentrically terraced as at 12. The disk has a central bore 14 to receive a shaft (not shown) by which it is rotated. When in use, the wheel is rotated at high speeds while a stream of slurry is fed down onto the upper face thereof. In order to break up the stream into very fine droplets, a row of pillars 16 is secured to the disk 10 near the periphery thereof. The tops of these posts are anchored against centrifugal forces by a ring 18. Since the surface of the disk 10 is subjected to securing and abrasion by the particles of clay which are fed on to the disk and then discharged centrifugally by the rotation of the disk, the life of the wheel is prolonged by coating the exposed surfaces with a layer 20 of a suitable wear resistant material such as a stable metal oxide. Metal oxides suitable for such purposes, for example, alumina, zirconia and 'spinel are found to be satisfactory materials for such coatings, these and other suitable oxides being mentioned in US. Patent No. 2,707,691, which patent also describes in detail a method of and apparatus for applying coatings of this kind in such a way as to make them stick properly. However, if such coatings are applied before the wheel has been rotated at the high speeds which will be employed in its ordinary use, the distortion of the wheel due to the great centrifugal forces acting on the disk is apt to cause the coating to crack and to chip off in places so as to expose portions of the surface of the wheel itself. I have discovered that by rotating the wheel at operating speeds prior to the application of the coating so that the wheel is centrifugally stretched and apparently assumes a set, coating applied thereafter lasts a great deal longer time. If preferred, the wheel may be initially coated and then rotated at service speeds until some chipping occurs, Then the coating is applied again to cover the exposed spots. This results in a durable coating but requires two separate coating operations.

It is evident that the principle of prestressing followed by the application of coating can be used in the coating of other objects and with other coating materials.

I claim:

The method of coating a metal spray wheel of approximately six-inch diameter for clay-drying apparatus, which comprises rotating said wheel at an operational speed of from 5,000 to 13,000 revolutions per minute whereby said wheel is centrifugally stretched and acquires a permanent set, stopping the rotation of said wheel, and coating said wheel with a thin layer of an abrasionresistant metal oxide.

References Cited in the file of this patent UNITED STATES PATENTS 607,624 Niedringhaus July 19, 1898 1,519,085 Barry et al. Dec. 9, 1924 2,707,691 Wheildon May 3, 1955 2,769,733 Pool Nov. 6, 1956 

